1. Field of the Invention
The present invention relates generally to electromagnetic relays and spot welding machines and, in particular, to a structure of an electromagnetic relay, in which a terminal having a vibration damping function is secured by spot welding to a plate spring fixed to a yoke and the terminal is secured to a base by insertion molding, and a spot welding machine for fixing the plate spring to a vibration damping portion of the terminal by spot welding.
2. Description of the Prior Art
A conventional technique for securing terminals and a yoke to a base of an electromagnetic relay is disclosed, for example, in Japanese Utility Model A-Sho 61-167349. The electromagnetic relay made by this conventional technique has terminals and an end of an L-shaped yoke secured to a base by insertion molding with resin. One end of the yoke is secured to the base, and a plate spring having an armature is fixed to the other end of the yoke by means of screws. A vibration damping plate is disposed between the yoke and the terminal so that the yoke has a vibration damping structure. One end of the vibration damping plate is fixed to the yoke by means of screws, and the other end of the vibration damping plate is soldered to one of the terminals.
However, in the prior art electromagnetic relay, since the vibration damping plate and the terminal were separate members, the number of parts and the number of mounting steps were increased, which gave rise to increased costs.
Further, since the vibration damping plate was secured to the terminal by soldering, an assembly process was difficult. In addition, since the vibration damping plate was secured to the yoke by means of screws, there was a further problem created by an increased number of parts.
On the other hand, a conventional spot welding machine is known which includes a fixed lower electrode and a movable upper electrode. Materials to be joined by spot welding with the conventional welding machine are placed on the fixed lower electrode, and electric resistance welding is effected while applying a pressure to the spot welding materials by means of the upper electrode, which is movable upward and downward. The extremities of the two electrodes are flat. The electrodes are formed approximately in the shape of a frustum with a welding point on a center line of the electrodes.
In the prior art spot welding machine, since the upper electrode was movable only upward and downward and the extremities of the electrodes were formed approximately in the shape of a frustum with the welding point on the center line thereof, welding defects were produced which caused weak welds allowing welded materials to be separated.